Manufacture of leather



Patented June .4, 1929.

ROBERT HOWSON PICKARD DOROTHY JORDAN LLOYD, AND ALBERT EDWARD CAUNCE,

' OF LONDON, ENGLAND. I Y

MANUFACTURE OF LEATHER.

No Drawing. Application filed August 22, 1925, Serial No. 51,874, and in Great Britain A s t az 192 i.

This invention has reference to improvements in and relating to the manufacture of leather. I

This may be effected either bysteeping the prepared and wet skin, hide, or pelt (all hereinafter included in the term skin) in a liquid tanning material or by subjecting it to the action of formaldehyde gas which lat ter, being readily soluble in water, is thus made to permeate the wet skin in the form of a solution.

Our invention differs essentiallyfrom the foregoing in that We effect the tanning by a tanning agent in gaseous form which remains in that form throughout the tanning operation.

An important feature of our invention is that we first dehydrate the skin and then subject the dehydrated or dried skin to the action of a tanning agent in gaseous form.

The dehydration should be effected without bringing about shrinkage of the fibres of the skin and to this end we immerse the wet skin in a bath or may be successive baths of a volatile solvent of water. not injurious to the fibres of the skin and then evaporate off the solvent. Acetoneis a solvent of water eminently suitable for the purpose.

Instead of immersing the skin in a bath we may spray it with the solvent to effect its dehydration.

Formaldehyde vapour, or an inert gas or air saturated with formaldehyde, constitutes an excellent tanning agent when employed for effecting the tanning of dehydrated skins, but we wish it to be understood that our invention is not limited to this as other aldehydes (such as acetaldehyde), bromine, chlorine, or any of the numerous substances'which are known to tan in aqueous or alcoholic solution but which can also be conveniently and economicallyconverted into their gaseous forms, may be employed in carrying our invention into practice.

l/Vhen the dehydration of the skin has been effected. for instance by steeping it in successive baths of acetone of suitable strength and the'n evaporating off the acetone in the skin, the dry skin which is very porous is subjected to the action of a tanning agent in gaseous form and, owing to the porosity of the dry skin, said agent will readily permeate it and ifthe treatment be continued thorough tannage will result in a comparatively brlef period. v

' The skin thus converted into leather may now be dyed, stuffed, fat liquored, or subjected to any otherusual and desired finishing operation.

We now proposebyway of examples-to describe in greater detail the method to be adopted when goat pelt'and skin in the hair are to be tanned in accordance with our invention, the details appertainmg to the treatmentof these being sufficient to enable those skilled in the art to makethe necessary variations if different primary materials than those stated tanned.

In the case of .goat pelt, this in the bated condition is washed with cold water and is then dried by treatment with or in a bath or a succession of baths of acetone until in the final bath the pelt is in equilibrium with a mixture of water and acetone of density not greater than 0.810. (The thoroughness of the treatment can be conveniently-tested by cutting off a small piece of the pelt and if this after evaporation off of the acetone at 135 Fah. (57 cent.) wets back rapidly with water the treatment is complete). The excess of acetone is then drained off and the acetone remaining in the peltevaporated in acurrent-of air or inert gas which may be (for instance hide) are to be heated up to a convenient temperature of 1359 Fah. (57 cent).

The pelt so prepared may at once be subjected to the further treatment to be described, or it may be stored until it is convenient to treat it.

The further treatment consists in packing or suspending the pelt in the above very porous conr ition in a suitable container through which, by suction or pressure, is passed a current of air or inert gas containing mixed with it the formaldehyde or other tanning agent in the gaseous or vapour state. A suitable mixture is obtained by bubbling the air through a solution of formalin in water which may be warmed. Or the formaldehyde may be used in the gaseous form without admixture with air.

The leather thus produced retains its substance, that is to say it loses nothing or at any rate very little in volume as compared with v place very readily and a very white and supple leatherwill result.

It is of course essential that the treatment with the tanningagent ingaseous form be continued long enough to complete the tannage and this may conveniently be determined by testing a sample piece by wetting back with water and then drying out. If the wet back test piece retains its substance and white oqaque appearance after it'is dried out in air, the tannage is complete.

When haired skins are to be tanned in ac cordance with out invention we proceed as follows:

' The skins,v after preliminary wet work such as washing soaking back with water or the like, and the usual short amount of treatment with alkalies such as caustic soda in dilute solution of lime, is then delimed with weak dilute acid solution such as borasic acid, so that the skin is in equilibrium with a solution of reaction pH about that usually used in the bati-ng operation, namely between pH=5.5 and pH=8.5 preferably pH =7. The skins may then be washed with water if desired, and then dried by the process of acetone treatment previously described.

The skin so prepared is then subjected to the action of the tanning agent in gaseous form as in the case of goat pelt and the sufficiency of the treatment may be ascertained by a similar test.

The tanning completed the resultant leather is eminently suited for dyeing, fatliquoring, and/or other usual finishing treatment.

more supple than those whereof the haired skin is treated in'the known manner.

1. The manufacture of leather by subjecting a dehydrated skin to the action of formaldehyde vapor.

2. The manufacture of leather by removing from a skin its water content by immersing the wet skin in acetone and then evaporating off the acetone so as to leave the fibres of the skin in the open condition, and then subjecting it to the action of formaldehyde vapour.

3. The manufacture of leather by treating a skin with acetone, evaporating off the ace tone from the skin, and then subjectingthe skin to the action of formaldehyde vapor.

4. The manufacture of leather by immersing a skin in acetone until it is in equilibrium with a mixture of acetone and water of specific gravtiy not greater than 0.810, evaporating off the acetone from the skin and subjecting it to the action of formaldehyde vapor. I I

5. A'process of manufacturing leather according to which the tannage of the leather is effected by treatment whilst in dry condition with formaldehyde-vapour which is in gaseous form throughout the tanning operation.

ROBERT HOVVSON PIOKARD. DOROTHY JORDAN LLOYD. ALBERT EDWVARD CAUNOE. 

